It is relatively common in log4j and extras for both appenders and receivers to add properties to events (see the use of the 'application' socketappender property in log4j).

There is an implementation detail in log4j's LoggingEvent that caused me to have to 'wrap' the logging event for use in Chainsaw: LoggingEvent provides a read-only copy of properties. 

Chainsaw uses the properties mechanism itself in order to support the dynamic rendering capabilities it provides.  Events in Chainsaw can be rendered differently based on the time delta from the previous displayed row, which changes when the display filter is updated.

If you can provide a way for me to update properties, I'd use whatever API you gave me.


On Mon, Aug 6, 2012 at 12:42 AM, Ralph Goers <> wrote:
If I understand what you are doing correctly, you are receiving a serialized LogEvent however it may have been delivered, possibly embellishing it and then passing it on to be logged.  If that is correct you are going to have to be tied to the implementation (i.e. core) as that is the only place a LogEvent exists. However, ideally core should provide what you need in a form such as AbstractServer but with a hook to let you modify the event.

Would that do what you want?  

Yes, I'm sure the javadoc could be improved.  I would request you either open a Jira, fix it, or both.


On Aug 6, 2012, at 12:31 AM, Scott Deboy wrote:

ok, LogEvent is an interface, but in core.  And I'm coding the receivers against that interface, which says it returns a copy but does not in Log4jLogEvent:

     * Get the MDC data.
     * @return A copy of the Mapped Diagnostic Context or null.

By the way, the class javadoc for ThreadContext is incomplete or incorrect.

 * The ThreadContext allows applications to store information either in a Map
 * <p/>

So, I need a new API that doesn't return a copy? Or do I have to create a copy of an event when I add properties?

On Sun, Aug 5, 2012 at 11:21 PM, Ralph Goers <> wrote:
I'm confused. Although the javadoc could be better and both say they return a copy.  ThreadContext doesn't have methods named getContextMap or getContextStack.

Note that the LogEvent is not available in the API.


On Aug 5, 2012, at 10:45 PM, Scott Deboy wrote:

My point was really the contract in the API javadoc should be updated and we should implement that contract..if we neeed new APIs, that's ok..or if I'm forced to create a new Log4jevent I'll deal with the contract.


On Sun, Aug 5, 2012 at 9:32 PM, Ralph Goers <> wrote:
In the Log4j 2 API the getContext and cloneStack methods of ThreadContext return copies of the Map and Stack.  In the LogEvent in impl getContextMap and getContextStack return the actual Map and Stack that are in the LogEvent. Copying them would be too expensive.

I don't know that there are any components yet that can add, delete or modify MDC keys or values, but i know that such a feature would be desired.  That said, the RewriteAppender uses the RewritePolicy which creates a new LogEvent.


On Aug 5, 2012, at 7:16 PM, Scott Deboy wrote:

> Chainsaw and some Receivers add properties to events to support tracking, for example, log4jid is added by Chainsaw.
> One thing that needs to be clarified in the api contract is whether or not getContextMap and getContextStack give you a copy of the map/stack or the original, as again, Chainsaw and others will need to use some api to modify those values.
> Scott

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